INFLUENCE OF INCREASING DIETARY CATION-ANION BALANCE ON THE PERFORMANCE OF LACTATING DAIRY CATTLE

Twelve mid-lactation Holstein cows were blocked according to milk production and assigned to diets containing +12, +29, +54, or +64 meq [ (Na+ +K+ )- C1- ] 100^-1 g diet dry matter (DM). The objective of this study was to examine diets having cation-anion balances spanning a range wider than had been examined previously. Diets were mixed to contain a 60:40 concentrate to corn silage ration (DM basis). Treatment periods were 3 wk with the first 2 wk serving as an adaptation period. Feed intake, actual milk yield, milk fat, fat yield , and 3.5% FCM increased as dietary cation- anion balance increased to +54 meq 100^-1 g DM. Blood pH, PCO2 and HCO3increased with increasing dietary cation-anion balance. Plasma Na^+, K^+, and Mg^2+ levels were unaffected by the dietary treatment. Urinary pH was lower for cows fed the +12 diet than for those fed all other diets. Urinary Na^+, K^+ the +12 diet excreted more Cl^- and Ca^2+ in urine compared with those fed all other treatments. Ruminal pH was not affected by the dietaary treatment. Fermentation patterns were only slightly affected by the dietary cation-anion balance. The results suggest that dietary cation-anion balance may become a useful tool when examining the overall performance of lactating dairy cattle.